Journal of the Royal Society
of New Zealand abstracts
A New Zealand climatic
template back to c. 3.9 Ma: ODP Site 1119, Canterbury Bight, south-west
Pacific Ocean, and its relationship to onland successions
Robert M. Carter
Marine
Geophysical Laboratory, James Cook University, Townsville, Australia,
and School of Earth and Environmental Sciences, University of Adelaide,
Adelaide, Australia.
Email: bob.carter@jcu.edu.au
Abstract Ocean
Drilling Program Site 1119 is located east of South Island, New
Zealand, in 394 m water depth on the upper continental slope.
Though 93 km offshore today, during recent glaciations the
site lay near the lowstand shoreline, directly beneath the path of
seasonal riverine meltwater plumes. The core comprises an upper portion
(0–86.19 metres composite depth (mcd)) deposited as upper
slope clinoforms and a lower portion (to 513.5 mcd) deposited
as mid-slope, intermediate water depth sediment drifts, the two
intervals being separated across a short c. 25 k.y. long unconformity
within Marine Isotope Stage (MIS) 8. Almost throughout, the core
comprises alternating micaceous muds and silts (glacials) and muddy,
sometimes calcareous, sands (interglacials). Because of the enhanced
potassium content of the terrigenous muds, the lithologies that
characterise the two different climatic states possess markedly
different natural gamma radiation signals, high and low, respectively.
The natural gamma profile of Site 1119 therefore provides a high
quality climatic time series with a 1–2 k.y. resolution (as sampled)
back to the mid-Pliocene. The cyclic gamma ray pattern provides a proxy
measure of ice volume in the Southern Alps, and is therefore an
atmospheric record. This record matches closely that of oceanic oxygen
isotope curves back to MIS 100 (2.4 Ma) and less closely beyond to MIS
Gi-11 (3.91 Ma) at the base of the core. Marked, high gamma ray
intervals at 3.68–3.63, 3.38, 3.12, and 2.80–2.67 Ma may reflect sharp
mid-latitude atmospheric coolings at these times, as supported by
marine faunal and isotopic evidence elsewhere in the New Zealand
region. Alternatively, they may in part reflect changes in clay
provenance consequent upon tectonic uplift in the hinterland. The
natural gamma measurements are consistent with an overall decline of
6°C in average atmospheric temperature over South Island, New
Zealand, since 2.45 Ma. Milankovitch 41 k.y. cyclicity is also
prominent in the natural gamma record over this period, and its 60 API
unit magnitude implies temperature swings up to 12°C between
glacials and interglacials (G/I). Similarly large G/I temperature
changes occur also in nearby sea surface temperatures east of South
Island and in atmospheric temperatures in Antarctica (Vostok),
suggesting that Pleistocene climate signals were closely synchronised
across wide areas of Southern Hemisphere middle and high latitudes.
Together with changing tectonic and related palaeogeographic patterns,
these temperature changes must have played a significant role in
influencing the local time ranges of taxa used in biostratigraphy. Very
few, if any, traditional New Zealand Pliocene-Pleistocene index fossils
have synchronous ranges across the region, and other methods of
correlation (magnetostratigraphy, cyclostratigraphy, tephrochronology,
isotope stratigraphy, and numeric dating) have therefore come to be of
particular importance. The Site 1119 natural gamma record provides a
unique reference template for climate variation in New Zealand
mid-latitudes, with which are compared the available correlation
markers for both onshore and offshore Pliocene-Pleistocene strata in
the New Zealand region.
Keywords Ocean
Drilling Program; ODP Site 1119; Canterbury Drifts; Canterbury Bight;
climate change; natural gamma radiation; Pliocene-Pleistocene; stage;
New Zealand
R04012 Received 30 July 2004;
accepted 18 May 2005; Online publication date 27 July 2005
Journal of the Royal Society
of New Zealand
Volume 35, Number 1 & 2 March/June, 2005, pp 9–42
PDF file of entire paper: Print-quality
(1030K) | screen-quality
(1347K)
This year's abstracts
|
Journal
home page |
All abstracts
|
Publishing
home page
